Summary

The ultrastructure of the choanoflagellate Codosiga botrytis is described with particular reference to the flagellar appendages, the flagellar rootlet system, the transition zone, the basal body and accessory centrioles, and the stalk. The controversial early reports of flagellar appendages in this species have been confirmed and they have been detected in 2 further species, Salpingoeca frequentissima and Monosiga sp. The appendages consist of a delicate bilateral vane 2 mum wide on either side of the axis, composed of extremely fine overlapping or interwoven fibrils. The flagellar root system consists of a large number of radiating microtubules associated with bands of electron-dense material near the basal body; striated roots are absent. The microtubules extend from several separate foci, those in any one group originating near a composite electron-dense band, and for a distance of 300 nm from the basal body they are separated by blocks of interstitial material. The flagellar basal body forms one of a diplosome pair of centrioles. The triplet microtubules of the accessory centriole are embedded in amorphous electron-dense material and the whole is enveloped in a sheath of similar appearance. The existence of a third centriole close to the diplosome pair is also reported. The relatively complex structure of the flagellar transitional zone is described. The stalk is composed of a core of circular lacunae, which may or may not contain finger-like protoplasmic extensions of the posterior end of the cell, surrounded by a continuation of the sheath material which encloses the remainder of the protoplast. In the stalk only there is a further closely sheathing layer about 15 nm thick which is regularly striated, the spacing of the striations in shadowcast material and sections being about 3 times that measured by negative staining. The structure of choanoflagellates differs widely from that of the algal class Chrysophyceae, the group in which they are included in some classifications, and from the remainder of the algae; they do not appear to have a place in either the algae or the plant kingdom. The structure of Codosiga botrytis is briefly compared with that of sponge choanocytes and collared cells in the Metazoa and some of the possible phylogenetic implications of this are indicated.

Pavan Vedula and Anna Kashina propose a new concept, the actin code, which encompasses the regulation of the essential functions of mammalian actins at the nucleotide level, rather than at the level of amino acids.

“To me, there are no real boundaries between chemistry, biology, physics and maths.”

Tony leads a group at the Mechanobiology Institute in Singapore, focusing on dissecting the structure–function relationship that underlies protein complexes that are involved in cell migration and adhesion. He shares his thoughts on why you don’t necessarily have to choose between the different branches of science that you find fascinating.

We also feature interviews with first authors of a selection of papers published in Journal of Cell Science, helping early-career researchers promote themselves alongside their papers. Check out our recent First Person interview with Julia Abitbol.

The second in our series of cell dynamics meetings now turns to organelles. This May 2019 meeting in Lisbon, Portugal, aims to bring together scientists studying the interface between organelles and the cytoskeleton at different scales and perspectives using a range of model systems. Find out more and register your interest here.

We are currently seeking proposals for four Workshops to be held in 2020. Do you have an idea for a Workshop? Please let us know and you could be one of our 2020 Workshop organisers. You focus on the science, we focus on the logistics. We are particularly keen to receive proposals from postdocs. Deadline date for applications is 25 May 2018.

Meet the preLighters! In the latest interview with our preLights community, the preLights team caught up with James Gagnon, Assistant Professor at the University of Utah, to talk about his research, how science can be made more open, his enthusiasm for the preLights project and the fun sides of being a junior PI.

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Where could your research take you? Join Alexander and apply for the next round of Travelling Fellowships from JCS by 25 May 2018.